A bad fluid temp sensor would definately keep the trans from shifting into overdrive. The tcu uses the sensor as a safeguard. ShIfting into overdrive and allowing the torque convertor to lock up before the temps are at temp is not good. Ive heard of a few issues related to this. First the sensor is located in the valve body with the solenoids i believe. The sensor itself could be bad, but ive also seen the ground lug pull loose from the valve body and cause this. If uou unbolt the lug and tug on the wire it should be very snug. If not resolder it. As far as testing the sensor, it is a neg coeffient sensor, so testing shouldnt be any different than say an ECT. Hope this was helpful
......And just as they're about to catch me.....Twin......Turbos......Kick.......In!
